Detailed studies of tumor-host immune interactions in animals and humans with sarcomas are being performed in an attempt to develop new immunodiagnostic and immunotherapeutic techniques for diagnosis and treatment of these tumors. Immune response to murine sarcomas has been extensively evaluated and both tumor- specific and fetal antigens have been identified. Attempts are being made to develop adoptive immunotherapeutic techniques utilizing transfer of cells grown in long term culture in T cell growth factors. Techniques for the prolonged growth of cytotoxic and proliferative T cells have been developed. These cells have been shown to mediate immunologic rejection of allografts and syngeneic tumors and attempts to use these cells for the adoptive immunotherapy of mouse and human tumors are in progress. The systemic administration of Interleukin-2 has been shown to enhance immune responses in vivo and therapeutic trials of IL-2 in humans will be undertaken shortly.